For FSX/FSX Steam and P3D, those sims favour Intel and Nvidia they really do, so many tweaks can be done with Nvidia inspector for them in particular.

Both sims (they are related) are very CPU dependant, you mention the choice of DD3 or DDR4 depending on chipset/CPU you choose, so if upgrading I'd go DDR4, its relatively cheap now and is the way forward ... I have to dash out just now or would have written more, but if you see this and would like more advice from a massive FSX/P3D flight sim enthusiast who builds performance PC's mainly for these sims, answer the thread and I should see a notification if you need more detailed enthusiast advice